The present invention relates to a digital signal processor suitable for a color video camera using a charge-coupled device (CCD) achieving simultaneous scanning of two lines of mixed or interlaced pixels.
An example of a digital signal processing in a video camera related to the present invention has been described in the JP-A-63-45153.
In the video cameras, solid-state imaging devices are arranged in various kinds of configurations primarily classified into a metal-oxide semiconductor (MOS) type and a CCD type. In general, an MOS-type sensor has plural output lines, whereas a CCD-type sensor possesses a single output line. For digitalization of signal processing, the CCD-type sensor of the single output line requires only one analog-to-digital (A/D) converter and is hence advantageously used as compared with the MOS-type sensor necessitating many A/D converters. Furthermore, the CCD-type sensors are configured in various methods. At present, there has been commonly employed a CCD sensor which operates in a mixed or interlaced pixel read method and which has been described in pages 1 to 6 of the Technical Report of the Institute of Television Engineers of Japan, TEBS101-1, ED836. This CCD image sensor is different in the constitution from the CCD image sensor described in the JP-A-63-45153. However, for the CCD sensor, the signal processing can be digitalized by adopting the similar processing.
In a video camera using the CCD image sensor operating in the mixed pixel read method, color difference signals respectively associated with R-Y and B-Y signals are originally generated for each horizontal scanning. Either one of the color signals which is not produced is interpolated with a color difference signal produced in the horizontal scanning period (i.e. before the 1H period), thereby obtaining the R-Y and B-Y signals for the current line undergoing a horizontal scanning. In this description, letters R, B, and Y stand for a pixel signal of red, a pixel signal of blue, and a luminance or brightness signal, respectively. Due to the processing above, the following problems arise with respect to the picture quality.
1) The line interpolation leads to different sampling points of color difference signals and hence the vertical resolution is lowered.
2) The signal processing inherent to a camera in which the red (R), green (G), and blue (B) signals undergo a .gamma. processing to produce color difference signals from resultant signals is not conducted. Consequently, the fidelity of color reproduction is deteriorated even when the quality of hue is not taken into consideration. Furthermore, the color matrix has a reduced degree of freedom and hence a color moire is likely to increase.
The video camera using the digital signal processing described in the JP-A-63-45153 also comprises the same fundamental constitution associated with the signal processing and hence has the similar problem.